The present invention relates to cutting tools for use in an apparatus for disintegrating material, such as a tree stump grinding machine.
Conventional stump grinders are disclosed in U.S. Pat. Nos. 5,135,035; 5,279,345; 5,497,815; 5,582,353; and 5,743,314, for example. A typical tree stump grinding machine comprises a rotatable wheel having a plurality of cutting assemblies mounted thereon. The wheel is rotated while adjacent to the stump, and the cutter teeth are moved into contact with the stump. As a result, the stump is gradually disintegrated.
A stump grinder of the type disclosed in U.S. Pat. No. 5,135,035 is depicted herein in FIG. 1. That cutter device 10 includes a rotary shaft 12 to which a hub 14 is attached. A plurality of cutters 16 is mounted around the outer periphery of the hub. Each cutter 16 includes a holder 18, and a cutter plate 20 soldered in a groove formed in an outer end of each holder 18. Each holder includes a fork-shaped base comprised of two parallel legs 22 (only one depicted). The legs straddle the hub and are secured thereto by a fastening screw 24.
A stump grinder of the type disclosed in U.S. Pat. No. 5,135,035 is depicted herein in FIGS. 2 and 3. That grinder 30 includes a holder 32 and a cutter bit 34 mounted therein. The holder 32 is adapted to be secured to a rotary hub (not shown). The cutter bit 34 includes a base 36 and a carbide cutting tip 38 affixed thereto. The base 36 includes a forwardly facing flat surface 40 having a center cylindrical pin 42 projecting forwardly therefrom. The carbide tip 38 has a center hole for receiving the pin 42, and a concavely recessed front face 44 bordered by a circular cutting edge 46. The cutting edge is formed by the intersection of the front face 44 and a side face which intersect one another at an acute angle a. The base 34 includes a cylindrical shank 48 mounted in a hole 50 of the holder 32 by a roll pin 52, permitting the cutter bit to rotate freely about its center axis x, thereby enabling wear to be distributed more evenly around the cutting edge. That is in contrast to the cutter of FIG. 1 wherein the plate 20 is stationary relative to the body in which it is mounted.
The cutter bit 34 of FIGS. 2-3 works satisfactorily when cutting in wood, but when the bit contacts the ground, e.g., to cut parts of the stump close to, or buried in, the ground, the cutting edge tends to quickly fracture, causing large chunks of the tip to fall off. Thus, catastrophic failure of the tip quickly occurs. Also, although the shank is mounted for free rotation in the holder, to produce more uniform wear around the cutting edge, the rotation of the shank induced by contact with the material being cut is somewhat haphazard and may not result in a satisfactorily uniform wear distribution, resulting in a premature failure of the tip.
Therefore, it would be desirable to provide a cutter bit which is less susceptible to catastrophic failure, and exhibits a more uniform wear distribution.
One aspect of the present invention relates to a cutting tip for stump cutting, which comprises a body formed of a hard material (for example, cemented carbide). The body has a rear supporting surface, a front cutting surface, and a side surface extending between the supporting surface and the cutting surface. An outer peripheral portion of the cutting surface and a forward portion of the side surface intersect one another at substantially a ninety degree angle to form a generally circular cutting edge. An inner portion of the cutting surface disposed radially inwardly of the outer peripheral portion is axially recessed relative to the outer peripheral portion. A center hole extends through the body from the cutting surface to the supporting surface. A plurality of circumferentially spaced, raised ribs extend generally radially along at least a portion of the cutting surface.
Another aspect of the invention pertains to a cutting bit which comprises a shank. The shank defines a center axis and has a rear mounting portion and front head portion. The head portion includes a front face having a center post projecting axially from the front face. A generally circular lip projects forwardly and extends around an outer periphery of the front face. The front face and the lip form a pocket surrounding the post. The post extends forwardly past the pocket. The lip engages a side surface of the cutting tip, and the post extends through the center hole of the cutting tip.
Another aspect of the invention pertains to a rotary cutter which comprises a rotary wheel, a holder mounted on the wheel and forming a bore, and a cutting bit mounted in the bore. The cutting bit comprises the shank and the cutting tip brazed thereto.